<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>async函数和await_解决回调函数地狱</title>
</head>

<body>
  <form>
    <span>省份：</span>
    <select>
      <option class="province"></option>
    </select>
    <span>城市：</span>
    <select>
      <option class="city"></option>
    </select>
    <span>地区：</span>
    <select>
      <option class="area"></option>
    </select>
  </form>
  <script src="https://cdn.jsdelivr.net/npm/axios/dist/axios.min.js"></script>
  <script>
    /**
     * 目标：掌握async和await语法，解决回调函数地狱
     * 概念：在async函数内，使用await关键字，获取Promise对象"成功状态"结果值
     * 注意：await必须用在async修饰的函数内（await会阻止"异步函数内"代码继续执行，原地等待结果）
    */
    // 1. 定义async修饰函数
    async function getData() {
      // 2. await等待Promise对象成功的结果
      const pObj = await axios({url: 'http://hmajax.itheima.net/api/province'})
      const pname = pObj.data.list[0]

      const cObj = await axios({url: 'http://hmajax.itheima.net/api/city', params: { pname }})
      const cname = cObj.data.list[0]
      
      const aObj = await axios({url: 'http://hmajax.itheima.net/api/area', params: { pname, cname }})
      const areaName = aObj.data.list[0]


      document.querySelector('.province').innerHTML = pname
      document.querySelector('.city').innerHTML = cname
      document.querySelector('.area').innerHTML = areaName
    }

    getData()
  </script>
</body>

</html>